1. Field of the Invention
The present invention relates generally to the design and fabrication of packages for semiconductor devices. More particularly, it relates to a ceramic semiconductor device package having an improved ground plane, enhanced interlead isolation, and improved lead impedance in order to reduce high frequency signal degradation within the package.
Recent advances in the design and fabrication of silicon bipolar devices provide for gate delays as low as a fraction of a nanosecond, producing operating frequencies in the gigahertz range. The packaging of such high frequency devices, however, promises to be problematic. Although packaging is only a part of the overall chip-to-chip communication system, signal degradation at the package level frequently accounts for a disproportionate share of the degradation in the overall system.
Signal degradation can arise from a variety of factors, including (1) variations in signal line impedance, causing signal reflections which are a major source of noise, (2) resistive losses in the internal package transmission lines, causing signal attenuation, (3) capacitive coupling between adjacent signal transmission lines, causing cross-talk which is another major source of noise, and (4) inductive coupling, particularly in the power and ground connections, causing waveform degradation and cross-talk between the various signals.
It would be desirable to provide semiconductor packages which minimize some or all of the degradative factors listed above. In particular, it would be desirable to provide ceramic semiconductor packages which minimize variations in signal transmission line impedance, minimize resistive losses in the signal transmission lines, reduce capacitive coupling between adjacent signal transmission lines, and reduce inductive coupling in the power and/or ground connections.
2. Description of the Background Art
U.S. Pat. No. 4,551,746 to Gilbert et al. discloses a ceramic semiconductor package having a metallized die attach pad connected to a metallization area by a via and a metallized castellation. Schaper (1981) Proc. First Annual Conference of the International Packaging Society, Cleveland, Ohio, Nov. 9-10, pp. 38-42, describes inductance problems which can arise in packaging high frequency semiconductor devices; see in particular .sctn. VIII. Copending U.S. patent application Ser. No. 557,119, now U.S. Pat. No. 4,680,613 assigned to the assignee of the present application, describes a low inductive impedance dual in-line package having a semiconductor device mounted on a ground plane separate from a lead frame. The ground plane is connected to the device ground.